Carbon dioxide (CO2) accounts for about 76% of global greenhouse gas emissions from human activities, with methane (16%), nitrous oxide (6%), and fluorinated gases (2%) accounting for the balance (United States Environmental Protection Agency). The majority of CO2 comes from the burning fossil fuels to produce energy, although industrial and forestry practices also emit CO2 into the atmosphere. Reduction of greenhouse gas emissions, particularly CO2, is critical to halt the progression of global warming and the accompanying shifts in climate and weather.
It has long been recognized that catalytic processes may be used to convert gases containing carbon dioxide (CO2), carbon monoxide (CO), and/or hydrogen (H2), such as industrial waste gas or syngas, into a variety of fuels and chemicals. Recently, however, gas fermentation has emerged as an alternative platform for the biological fixation of such gases. In particular, C1-fixing microorganisms have been demonstrated to convert gases containing CO2, CO, and/or H2 into products such as ethanol and 2,3-butanediol. Efficient production of such products may be limited, for example, by slow microbial growth, limited gas uptake, sensitivity to toxins, or diversion of carbon substrates into undesired by-products.
It has long been recognized that catalytic processes, such as the Fischer-Tropsch process, may be used to convert gases containing carbon dioxide (CO2), carbon monoxide (CO), and/or hydrogen (H2) into a variety of fuels and chemicals. Recently, however, gas fermentation has emerged as an alternative platform for the biological fixation of such gases. In particular, anaerobic C1-fixing microorganisms have been demonstrated to convert gases containing CO2, CO, and/or H2 into products, like ethanol and 2,3-butanediol.
Such gasses may be derived, for example, from industrial processes, including ferrous or non-ferrous metal products manufacturing, petroleum refining, gasification, electric power production, carbon black production, ammonia production, methanol production, and coke manufacturing. However, these industrial gasses may require treatment or recomposition to be optimized for use in gas fermentation systems. In particular, industrial gasses may lack sufficient amounts of H2 to drive net fixation of CO2 by gas fermentation and reduce CO2 emissions to the atmosphere.
High hydrogen streams are beneficial to fermentation products which have low energy demand and where CO2 can be used as a reactant, such as with ethanol production.
Accordingly, there remains a need for improved integration of industrial processes with gas fermentation systems, including processes for enriching the H2 content of industrial gases delivered to gas fermentation systems.